Note 8 - Segment and Geographic Information - Summary of Current Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019	Dec. 28, 2019
Net sales by segment:
Net sales	$ 144,084	$ 150,011	$ 283,005	$ 297,820
Segment profit (loss) before tax:
Profit (loss) for reportable segments	(320)	(13,660)	(10,899)	(27,685)
Interest expense	(3,456)	(5,282)	(7,883)	(10,789)
Interest income	21	191	168	413
Loss from continuing operations before taxes	(4,603)	(20,299)	(22,913)	(43,350)
Assets, Total	1,066,583		1,066,583		$ 1,077,710	[1]
Discontinued operations	0		0		3,618
Corporate, Non-Segment [Member]
Segment profit (loss) before tax:
Corporate expenses	(848)	(1,548)	(4,299)	(5,289)
Assets, Total	55,952		55,952		18,398
Semiconductor Test and Inspection [Member]
Net sales by segment:
Net sales	131,428	137,578	259,441	274,272
Segment profit (loss) before tax:
Profit (loss) for reportable segments	(2,331)	(14,400)	(13,904)	(29,444)
Assets, Total	948,659		948,659		998,756
PCB Test [Member]
Net sales by segment:
Net sales	12,656	12,433	23,564	23,548
Segment profit (loss) before tax:
Profit (loss) for reportable segments	2,011	$ 740	3,005	$ 1,759
Assets, Total	61,972		61,972		56,938
Semiconductor Test and Inspection and PCB Test [Member]
Segment profit (loss) before tax:
Assets, Total	$ 1,010,631		$ 1,010,631		$ 1,055,694

[1] Derived from December 28, 2019 audited financial statements